The present invention relates, in general, to fixtures for testing of electrical devices such as integrated circuits, and more particularly to a fixture which uses flexible printed circuit tape to make contact with integrated circuits mounted in tape automated bonded (TAB) packages.
Tape automated bonding of integrated circuits has allowed a significant increase in the packaging density of high performance integrated circuits. This advance in packaging technology has placed severe demands on fixtures designed to facilitate testing of the integrated circuits. These fixtures must make reliable contact with every lead of the package, but must not require a lengthy setup and must not cause wear or damage to the package. With as many as 1024 leads per package and a need for minimal lead length the lead spacing must be extremely small. In the past, fixtures for testing integrated circuits have consisted of special sockets designed for the purpose. With the advent of surface mount technology and tape automated bonded integrated circuits a variety of these special sockets have been devised using compressible pins of some sort. These sockets have proven adequate for pins as close as a 0 508 mm pitch, but this pitch appears to be close to the practical limit to this approach. It is not practical to manufacture sockets of this type with a constant 50 ohm impedance, nor is the compressible pin alignment easy to adjust. Finally, the insertion and removal of integrated circuit parts requires several manual steps making such sockets unsuited to a high volume testing application.
High density packages now require a fixture which can handle leads having a 0.2032 mm pitch and a 0.1016 mm width. Leads this small and packed this closely require precise lateral and vertical alignment of both the integrated circuit leads and the test fixture contacts. In addition, high speed circuits such as application specific integrated circuits (ASIC) built using emitter coupled logic (ECL) can require a signal bandwidth of 3 Ghz. With signals of this bandwidth a constant impedance throughout the entire signal path, including the test contact fixture, is essential for proper operation of the integrated circuit being tested.